Did some research and you are correct that by the time of the Muslim invasion the Christians of Spain were reasonably united, though in previous centuries there had been a lot of religious dissent.
However, the Visigoths were among the most anti-semitic of all the Christian nations of the time and persecuted the Jews with great enthusiasm. Hence, it is recorded that the Jews opened the gates of Toledo to the Muslims, accurately seeing them as likely to treat them with greater lenity than did the Christians.
In any case, it is obvious something was wrong with the Spanish of the time. They were conquered in just a few years by a small army at the end of a very long supply line.
800 years or so before the Romans needed a couple of centuries to conquer Iberia, and of course Napoleon learned just how hard it was to control the peninsula against the wishes of its people.
Very little of this resistance by the people occurred when the Moops (pop culture reference) invaded. Religious disaffection may not have been the reason, but obviously the people were not willing to fight and die against the invaders. This is probably because the Visigoths, something like 1% or 2% of the population, had retained all power and privilege in their own hands for several centuries. The people saw little reason to be concerned which group held this power. Which just goes to show that tyranny and oppression often sows the seeds of its own destruction.
good points